The present invention relates to a positioning system using GNSS (Global Navigation Satellite System) and a receiving terminal for use therein.
It has been known that GPS (Global Positioning System) as one of GNSS is used for positioning. As its positioning method, known is a static method of determining a position of a location (a positioning target location) with GPS receivers, which are capable of receiving a radio signal from a GPS satellite, installed at both the positioning target location and a location used as a reference (reference location) in a fixed manner.
In the static method, positioning data extracted based on a radio signal received by each GPS receiver (hereinafter referred to as positioning data acquired from each GPS receiver) is analyzed, thereby allowing the position of the positioning target location to be correctly determined. However, since high arithmetic capability is required for the analysis, an arithmetic processor for analyzing each positioning data is large-scale and bringing the arithmetic processor to a positioning field is difficult. Accordingly, in the static method, each acquired positioning data is brought back from the positioning field and is analyzed by the arithmetic processor to determine the position of the positioning target location.
However, in the aforementioned method, whether the acquired positioning data is satisfactory enough to correctly determine the position of the positioning target location from an analysis result acquired by analyzing the acquired positioning data by the arithmetic processor. When the data is not satisfactory enough to correctly determine the position of the positioning target location (a case where the position of the positioning target location cannot be correctly calculated), an operator needs to return to the positioning field and reacquire the positioning data from the beginning using each GPS receiver.
For that reason, for example, Japanese Patent Application Publication No. H10-267656 discloses that one type of positioning system has been proposed in place of bringing back positioning data acquired by each GPS receiver. In this positioning system, the positioning data is transmitted to an arithmetic processor by a communication unit. In addition, the arithmetic processor that receives the positioning data analyzes the positioning data, is configured to determine whether a position of a positioning target location is correctly obtained from the positioning data, and to transmit a warning signal to the GPS receiver if the position of the positioning target location is not correctly obtained. In this configuration, the GPS receiver is also configured to issue a warning upon reception of the warning signal.
This positioning system allows the operator to find out whether positioning data is satisfactory enough to correctly determine the position of the positioning target location while staying at the positioning field after acquiring the positioning data using each GPS receiver. This enables the operator to save time which would be otherwise spent traveling back and forth between the positioning field and a location where the arithmetic processor is placed. This also enables the operator to acquire positioning data again at the same positioning target location using each GPS receiver when the position of the positioning target location is not correctly obtained, and to acquire positioning data at a different positioning target location using each GPS receiver when the position of the positioning target location is correctly obtained. As a whole, with this positioning system, speedy positioning work is possible.
However, in the aforementioned positioning system, when the position of the positioning target location is not correctly obtained from positioning data acquired by each GPS receiver, positioning data on the same positioning target location needs to be reacquired from the beginning using each GPS receiver. This duplicates positioning data acquisition work at the positioning target location and, as a whole, efficiency of positioning work will be lowered.